UNIVERSITY  OF  CALIFOBNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


PRUNING  YOUNG  OLIVE  TREES 


BY 

FREDERIC  T.  BIOLETTI 


BULLETIN  No.  348 

September,  1922 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY 

1922 


David  P.  Barrows,  President  of  the  University. 

EXPERIMENT  STATION  STAFF 
HEADS   OF  DIVISIONS 

Thomas  Forsyth  Hunt,  Dean. 

Edward  J.  Wickson,  Horticulture  (Emeritus). 

,  Director  of  Resident  Instruction. 

C.  M.  Haring,  Veterinary  Science,  Director  of  Agricultural  Experiment  Station. 

B.  H.  Crocheron,  Director  of  Agricultural  Extension. 

C.  B.  Hutchison,  Plant  Breeding,  Director  of  the  Branch  of  the  College  of 

Agriculture  at  Davis. 
H.  J.  Webber,  Sub-tropical  Horticulture,  Director  of  Citrus  Experiment  Station. 
William  A.  Setchell,  Botany. 
Myer  E.  Jaffa,  Nutrition. 
Ralph  E.  Smith,  Plant  Pathology. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 
John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Fruit  Products. 
Warren  T.  Clarke,  Agricultural  Extension. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
Walter  Mulford,  Forestry. 
James  T.  Barrett,  Plant  Pathology. 
Fritz  W.  Woll,  Animal  Nutrition. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Reed,  Plant  Physiology. 
L.  D.  Batchelor,  Orchard  Management. 
W.  L.  Howard,  Pomology. 
•Frank  Adams,  Irrigation  Investigations. 

C.  L.  Roadhouse,  Dairy  Industry. 
R.  L.  Adams,  Farm  Management. 

W.  B.  Herms,  Entomology  and  Parasitology. 
John  E.  Dougherty,  Poultry  Husbandry. 

D.  R.  Hoagland,  Plant  Nutrition. 
G.  H.  Hart,  Veterinary  Science. 

L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Voorhies,  Assistant  to  the  Dean. 


DIVISION  OF  VITICULTURE  AND  FRUIT  PRODUCTS 

F.  T.  Bioletti  L.  O.  Bonnet 

W.  V.  Cruess  G.  Barovetto 

A.  W.  Christik  A.  J.  Winkler 

J.  H.  Irish  H.  E.  Jacob 


*  In  cooperation  with  Division  of  Agricultural  Engineering,  Bureau  of  Public  Roads,  U.  S. 
Department  of  Agriculture. 


PRUNING  YOUNG  OLIVE  TREES 

By  FREDERIC  T.  BIOLETTI 


CONTENTS 

I.  INTRODUCTION  page 

Objects  of  pruning 87 

Pruning  and  rate  of  development 89 

II.  INVESTIGATIONS 

The  experiments 91 

1.  The  trees 92 

2.  Pruning  at  planting 92 

3.  Pruning  the  first  year 92 

4.  Pruning  the  second  year 94 

5.  Pruning  the  third  year 94 

6.  Pruning  the  fourth  year 94 

7.  Pruning  the  fifth  year 94 

The  Results 96 

1.  Increase  of  circumference  of  trunk 98 

2.  Increase  of  height  of  tree 101 

3.  Increase  of  bulk  of  tree 101 

4.  Attainment  of  desired  form 102 

5.  Bearing 103 

III.  DEDUCTIONS 

Pruning  a  deterrent  of  growth 105 

Pruning  a  deterrent  of  bearing 105 

Minimization  of  pruning  the  ideal 105 

VI.  APPLICATION 

Development  of  young  trees 106 

Maintenance  of  bearing  trees 106 

V.  SUMMARY  AND  CONCLUSIONS 


I.     INTRODUCTION 

OBJECTS    OF    PRUNING 

The  pruning  of  an  olive  tree  has  two  purposes :  one,  to  give  it  the 
form  that  is  deemed  best  for  cultivation,  harvesting,  and  other  orchard 
operations ;  the  other,  to  regulate  the  size  and  the  quality  of  the  crop. 
In  pruning  a  young  olive  tree  before  it  commences  to  bear,  only  the 
first  of  these  purposes  is  considered.  The  object  should  be  to  give 
the  tree  the  desired  form  in  the  shortest  time,  and  to  do  this  as  econom- 
ically as  possible. 


88  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 

The  form  desired  must  be  clearly  in  the  primer's  mind  and  before 
he  can  hope  to  accomplish  his  object  he  must  understand  the  nature 
of  the  tree  and  how  it  will  react  to  each  operation. 

The  form  almost  universally  accepted  as  the  best  is  the  open  vase 
form.  This  consists  of  a  single  trunk  sufficiently  high  (2  to  3  feet) 
to  permit  of  close  cultivation,  with  3  to  5  main  branches  rising  from 
near  the  top  of  this  trunk  at  an  angle  of  about  60°  to  a  height  of  6  or 
7  feet  and  then  gradually  curving  outward  until  they  become  hori- 
zontal or  even  slightly  pendant.  These  main  branches  divide  repeat- 
edly into  secondarjr  and  tertiary  branches  and  so  on  until  they  reach 
the  final  division  called  twigs,  which  bear  the  leaves  and  the  'fruit. 
A  fully  formed  tree  of  this  kind  will  be  a  hollow  inverted  cone  com- 
posed of  branches  of  various  sizes  upon  which  the  bearing  twigs  form 
an  open  network.  The  interior  of  the  cone,  while  free  from  large 
branches,  should  be  well  supplied  with  small  branches  and  bearing 
twigs — in  fact,  all  parts  of  the  tree  should  be  well  supplied  with 
healthy  bearing  twigs.  This  can  be  accomplished  only  by  a  tree  of 
this  general,  open  vase  form,  which  allows  the  sunlight  to  reach  all 
parts. 

While  there  is  not  much  difference  of  opinion  as  to  the  best  form 
of  tree,  there  is  much  difference  of  both  opinion  and  practice  regard- 
ing the  best  method  of  obtaining  this  form. 

European  writers  describe  and  advise  very  painstaking  and 
detailed  methods  of  pruning  the  young  tree  several  times  during  the 
3rear,  with  the  object  of  forcing  it  to  take  the  desired  shape.  Much 
of  this  work  is  done  in  the  nursery  and  the  trees  are  usually  4  or  5, 
or  even  8  or  10  years  old,  before  they  are  planted  in  the  orchard. 
Calif ornian  writers  and  many  growers  adopt  similar  methods  though 
there  is  usually  little  pruning  in  the  nursery  and  the  trees  are  usually 
only  2  to  3  years  old  when  planted  out. 

The  method  commonly  adopted  by  careful  growers  in  California 
is,  each  year,  to  head  back,  more  or  less,  every  branch  of  young  olives, 
with  the  object  of  forming  a  solid,  stocky  framework  which  will  hold 
a  heavy  crop  and  resist  wind  damage.  In  heading  back,  the  cut  is 
made  just  above  a  side  branchlet.  The  branchlet  chosen  is  one  which 
points  in  the  direction  in  which  it  is  desired  to  have  the  branch  grow. 
On  upright  growers,  like  Mission,  an  outer  branchlet  is  left ;  on  spread- 
ing growers  like  Manzanillo,  an  inner  branchlet. 

Unfortunately  the  tree  seems  to  resent  this  interference  with  its 
natural  inclinations.  In  both  cases  the  strongest  branches  grow  in 
1 1  io  direction  the  tree  prefers,  so  that  it  is  usually  a  weak  branch  which 
the  pruner  must  choose  to  leave.     The  removal  of  the  strong  inner 


>48]  PRUNING  YOUNG  OLIVE  TREES  89 

branch,  in  the  case  of  Mission,  or  of  the  strong  outer  branch,  in  the 
case  of  Manzanillo,  creates  the  open  space  well  supplied  with  sunlight 
that  the  pruner  desires.  But  during  the  following  growing  season, 
this  space,  which  it  is  desired  to  keep  vacant,  is  filled  up  again  by  a  new 
vigorous  shoot.  This  new  shoot  grows  more  strongly  than  the  desired 
shoot  which  was  left,  because  it  is  following  its  preferred  direction. 
At  the  next  pruning  a  similar  attempt  is  made  by  the  pruner.  He 
removes  the  new  vigorous  shoot  and  retains  the  older  and  weaker  one. 
In  time,  by  very  severe  and  constant  pruning,  this  method  often 
results  in  a  fairly  well  shaped  tree. 

PRUNING  AND  RATE  OF  DEVELOPMENT 

There  is  some  difference  of  opinion  among  horticulturists,  both 
practical  and  theoretical,  as  to  whether  pruning  increases  vigor  or,  as 
it  is  sometimes  expressed,  ' '  devitalizes  the  tree. ' '  And  it  seems  worth 
while  to  inquire  whether  this  severe  pruning  does  not  stunt  or  at  least 
delay  the  development  of  the  young  olive. 

L.  H.  Bailey1  states  that  pruning,  even  when  somewhat  heroic,  is 
not  devitalizing  and  supports  this  opinion  with  various  a  priori  and 
observational  arguments. 

Babo2  states  that  investigations  at  the  Geisenheim  School  of  Horti- 
culture have  shown  that  unpruned  vines  much  surpass  those  pruned 
annually,  in  circumference  of  trunk  and  especially  in  size  of  root  sys- 
tem. He  also  gives  many  examples  of  pruning  practices  in  various 
parts  of  Europe  to  show  that  vines  which  are  pruned  lightly  and 
allowed  to  grow  somewhat  in  accord  with  their  natural  habit  are  more 
vigorous  and  more  resistant  to  disease  and  injuries  than  vines  pruned 
heavily  in  the  usual  way. 

P.  Pacottet3  states  that  a  pruned  vine  has  certainly  a  shorter  dura- 
tion of  life  than  one  not  pruned. 

Recently  much  convincing  evidence  has  been  supplied  by  the 
researches  of  J.  C.  Whitten  and  others  to  show  that  pruning  is  essen- 
tially a  "devitalizing"  process,  if  by  this  term  we  mean  that  it  cur- 
tails the  activities  of  the  plant  as  manifested  by  rapidity  of  growth 
and  early  bearing. 

Most  or  all  of  this  evidence  is  based  on  work  done  with  deciduous 
trees.  It  remains  to  be  seen  whether  the  pruning  of  trees  whose  leaves 
last  more  than  a  year  and  which  are  therefore  never  completely  bare 
has  similar  effects. 


i  The  Pruning  Boo};,  ed.  2,  1899,  pp.  5-12;  ed.  18,  1916,  pp.  6-14. 

2  Babo  and  Mach,  Weiiibau  und  Kellerwirschaft,  ed.  3,  1910,  pp.  625. 

3  P.  Pacottet,  Viticulture,  1905,  p.  193. 


90  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

G.  Foex4  states  that  the  activity  of  a  plant  or  of  a  branch,  other 
conditions  being  equal,  is  the  greater  the  larger  the  number  of  leaves 
it  bears.  This  statement  seems  to  be  based  on  a  correct  view  of  the 
principles  of  plant  physiology  involved.  To  be  more  exact,  perhaps 
it  should  include  also  the  time  during  which  the  leaves  function. 

If  we  accept  this  modification  of  the  statement  of  Foex  we  should 
expect  that  the  weakening  or  retarding  effect  of  pruning  would  be 
greater  on  evergreen  than  on  deciduous  trees.  When  we  prune  a 
deciduous  tree  we  simply  remove  a  certain  part  of  the  buds,  of  which 
Bailey  estimates  that  only  20  per  cent  would  grow  if  no  pruning  were 
done.  The  actual  number  of  buds  which  grow  in  each  case  may  be 
expected  to  be  approximately  the  same,  also  the  resulting  shoots  and 
leaf  surface,  and  consequent^  the  growth  and  vigor  of  the  tree  during 
the  ensuing  season,5  if  no  other  factor  is  concerned  than  the  number 
of  buds  which  develop.  When  we  prune  an  evergreen  tree,  on  the 
other  hand,  we  remove  leaves  which  are  actually  adding  to  the  vigor 
and  bulk  of  the  tree  or  which  are  ready  to  function  as  soon  as  the 
temperature  is  sufficiently  high.  This  places  a  great  handicap  on  the 
pruned  trees  which,  however  many  new  shoots  they  may  produce,  will 
require  weeks  or  months  to  develop  a  leaf  surface  equal  to  that  with 
which  the  unpruned  trees  commence. 

These  theoretical  considerations  are  supported  by  observations  on 
the  growth  of  young  olive  trees  under  the  various  systems  of  pruning. 
Nursery  trees  given  the  elaborate  and  continuous  pruning  practiced 
in  Europe  are  several  years  longer  in  reaching  the  size  attained  by 
trees  grown  in  California  in  nurseries  where  they  receive  little  or  no 
pruning.  Olive  trees  planted  as  wind  breaks  on  the  border  of  orchards 
of  other  trees  are  often  left  without  pruning  and  their  quick  develop- 
ment has  been  noted. 

In  spite  of  all  the  evidence  tending  to  show  that  pruning  depresses 
the  vigor  of  plants  of  all  kinds,  the  belief  in  an  invigorating  effect  of 
pruning  is  very  general  among  both  growers  and  horticultural  writers 
and  is,  in  its  turn,  supported  by  much  evidence.  The  renovation  of 
old  orchards  by  severe  cutting  back ;  the  removal  of  all  buds  but  one 
on  a  young  vine  to  insure  a  long  vigorous  shoot;  the  severe  pruning 
of  weak  vines  and  the  light  pruning  of  strong  vines  are  all  common 
and  accepted  practices.  On  the  other  hand,  the  weakening  and  even 
the  death  of  fruit  trees  and  vines  following  failure  to  prune  are  fre- 
quently observed. 

*  Cours  complet  de  viticulture,  ed.  4,  1895,  p.  379. 

5  That  dormant  pruning  of  decidous  trees  has  a  retarding  effect  has  been  shown 
by  J.  C.  Whitten  and  others,  but  this  does  not  affect  the  argument.  Any  other 
factors  which  enter  into  the  problem  may  be  expected  to  occur  in  the  case  of  ever- 
green trees,  also. 


Bulletin  348]  PRUNING  YOUNG  OLIVE  TREES  91 

This  paradox  is  easily  explained  by  two  considerations.  One  is 
that  the  activity  and  the  amount  of  growth  of  individual  shoots  does 
not  necessarily  indicate  a  corresponding  vigor  of  the  whole  plant.  A 
small  number  of  vigorous  shoots  may  represent  less  total  activity  in 
the  plant  than  a  larger  number  of  less  vigorous  shoots.  The  other  is 
that  pruning  when  sufficient^  severe  not  only  decreases  the  number 
of  vegetative,  leafy  shoots  produced,  but  decreases  the  amount  of  fruit. 
The  production  of  a  large  crop  may  absorb  so  much  of  the  energies  of 
the  plant  that  the  amount  of  leaf  surface  produced  where  the  pruning 
is  light  may  be  less  than  where  it  is  heavy.  Moreover,  the  development 
of  the  fruit  may  also  absorb  so  much  of  the  nutritive  material  elabor- 
ated by  the  leaves  that  the  plant  is  starved. 

During  the  formative  or  pre-fruiting  period  of  the  life  of  a  tree 
the  complication  of  crop  production  does  not  enter  and  the  problem 
is  much  simplified.  In  order  to  devise  a  suitable  method  of  pruning 
young  olive  trees,  the  specific  effect  of  the  severity  of  pruning  on  vigor, 
shape,  and  rate  of  development  uncomplicated  by  fruit-bearing  or 
other  disturbing  causes  must  be  known.  To  determine  this  an  investi- 
gation was  commenced  at  Davis  in  1917  and  has  yielded  interesting 
results  which  point  the  way  to  a  method  of  pruning  which  seems  more 
effective  and  more  economical  than  any  now  in  general  use. 

II.     INVESTIGATIONS 

THE    EXPERIMENTS 

In  April,  1917,  three  rows  of  olive  trees  were  planted  at  the  Uni- 
versity Farm,  Davis,  on  a  piece  of  deep,  level  loam  soil  from  which  an 
old  Muscat  vineyard  had  been  removed  one  or  two  years  before.  The 
rows  are  36  feet  apart  and  the  trees  12  feet  apart  in  the  rows.  (See 
Fig.  1.)  A  row  of  very  large  Black  Walnut  trees  is  growing  48  feet 
from  the  north  end  of  the  rows  and  has  had  a  depressing  effect  on  the 
first  two  or  three  trees  of  each  row. 


**  UDPING 

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_j  MISSION 

^    3  •  o  a    i    o  ii    i   o  it   i    o  ii   i   a  ii    i  o   ii    i  o   ii    i   o  H   »  o   it    i   o  if   i   o    ii   i   o  \i   i    ° 
5  MIHION 

I 

•    L^  I  O  l|  I   O  II  I  O  II  I  O     II  I  O  II   I  O  II  I  G     II  I  O  ll  l  O     II   (  O    II  I  O     II  1  0  II  - 

"■  Ml  S  S  I  0  N  *~ 

-*    S __.f- 

**  ASCOLANO 


Fig.  1. — The  Experiment  Plot. 


92  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

The  previous  preparation  and  the  annual  tillage  of  the  plot  have 
been  fair. 

During  the  first  year  an  irrigated  intercrop  of  corn  was  grown. 
In  the  spring  of  the  second  year  two  rows  of  vines  were  planted 
between  the  rows  of  olive  trees.  Since  the  second  year  the  rainfall 
has  been  deficient  and  the  trees  have  received  very  little  irrigation. 

The  trees  on  the  whole  have  done  well  though  the  combined  effects 
of  close  planting,  intercrops,  and  deficient  moisture  have  resulted  in 
less  growth  than  the  favorable  conditions  of  soil,  temperature,  and 
location  are  capable  of  producing. 

Difficulties  of  cultivation  have  also  resulted  in  mechanical  injuries 
to  about  15  per  cent  of  the  trees  which  have  more  or  less  limited  their 
growth.  This  probably  accounts  for  the  abnormally  small  growth  of 
a  few  trees  in  each  lot. 

The  trees  were  subjected  to  a  heavy  frost  in  the  nursery  during 
the  winter  before  they  were  transplanted.  This  may  explain  the  dying 
of  8  of  the  108  trees  planted. 

1.  The  Trees. — The  trees  used  were  Mission,  grafted  on  Redding 
seedlings.  The  seedlings  were  grown  in  a  greenhouse  at  Berkeley  in 
1913,  planted  in  the  nursery  at  Davis  in  1914,  and  grafted  in  the 
nursery  in  1915.  The  grafted  trees  when  planted  in  the  experimental 
plot  were  2  years  old  from  the  graft  and  4  years  old  from  the  seed. 

2.  Pruning  at  planting. — The  trees  were  dug  out  of  the  nursery 
by  hand  and  the  roots  shortened  to  a  few  inches.  The  tops  were  then 
cut  back  to  from  20  to  24  inches,  according  to  their  size,  and  all  leaves 
removed. 

3.  Pruning  the  first  year. — In  the  winter  after  the  first  growing 
season  (1917),  before  new  growth  had  started  in  the  spring,  the  trees 
were  pruned. 

Every  third  tree  commencing  with  tree  1  (see  Fig.  1)  in  each  row 
was  pruned  heavily.  The  pruning  consisted  in  removing  all  twigs  and 
branches  on  the  trunk  except  2,  3,  or  4  of  the  largest  near  the  top. 
The  branches  reserved  were  then  cut  back  to  within  3  to  6  inches  of 
the  trunk.  (See  three  trees  at  top  of  Fig.  2.)  This  is  the  method 
commonly  used  by  most  careful  primers.  Such  heavy  cutting  is,  how- 
ever, becoming  less  common,  though  severe  shortening  of  the  reserved 
branches  is  still  generally  practiced. 

On  the  remaining  trees  all  new  growth  to  within  a  few  inches  of 
the  top  of  the  trunk  was  also  removed  entirely ;  but  all  the  remaining 
branches  and  twigs  were  reserved  and  not  pruned  in  any  way.  (See 
two  trees  at  bottom  of  Fig.  2.) 


Bulletin  348] 


PRUNING  YOUNG  OLIVE  TREES 


93 


Fig.  2. — First  winter.     Typical  trees,  January,  1918,  nine  months  after  plant- 
ing.    Top  row  heavily  pruned;  bottom  no  pruning. 


94:  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 

4.  Pruning  the  second  year. — During  the  second  growing  season 
(1918)  every  third  tree  commencing  with  tree  3  in  each  row  was  lightly 
summer-pruned.  This  pruning  consisted  in  topping  the  more  vigorous 
shoots  (Fig.  3,  2-12,  2-18,  3-15).  No  other  summer  pruning  was  done 
except  to  remove  *all  shoots  which  started  on  the  trunk  below  the 
branches  on  all  trees.  In  this  way  the  trunks  were  kept  clear  of 
growth. 

Typical  trees  were  photographed  on  May  29,  four  months  after  the 
winter  pruning.  Fig.  3  shows  that  a  depressing  effect  of  heavy  prun- 
ing is  already  evident  after  active  growth  for  a  few  weeks.  The  pruned 
trees  have  not  only  a  smaller  number  of  growing  tips,  but  the  growth 
of  the  individual  twigs  is  much  shorter  than  on  the  unpruned  trees. 
This  can  be  seen  plainly  by  comparing  the  heavily  pruned  trees,  2-10, 
2-16,  and  3-13,  with  the  unpruned,  2-12  and  2-18,  which  appear  in 
both  figures  2  and  3. 

At  the  end  of  the  second  growing  season  the  same  treatment  was 
continued.  The  series  commencing  with  tree  1  was  heavily  winter 
pruned  and  no  pruning  given  to  the  others.     (See  Fig.  4.) 

5.  Pruning  the  third  year. — The  treatment  during  the  third  year 
was  the  same  as  during  the  second,  except  that  in  winter  an  occasional 
vigorous  spreading  branch  low  down  was  removed  on  the  trees  which 
were  to  be  pruned  as  little  as  possible.  The  extent  of  this  pruning  is 
shown  by  the  fact  that  from  24  heavily  pruned  trees  the  branches 
removed  weighed  13.25  pounds,  while  from  24  unpruned  trees  only 
.5  pound  was  removed  in  all.  On  May  12,  1920,  25  months  after  plant- 
ing, the  circumference  of  each  tree  at  about  25  cm.  from  the  ground 
was  measured.  The  circumference  of  the  heavily  winter-pruned  trees 
was  only  63  per  cent  of  that  of  the  unpruned  trees  and  of  the  summer- 
pruned  trees  only  87  per  cent. 

6.  Pruning  the  fourth  year. — Since  nothing  seemed  to  have  been 
gained  by  summer  pruning,  it  was  decided  at  the  end  of  the  third  year 
to  omit  it  in  the  future  and  to  prune  heavily  the  trees  of  the  series 
beginning  with  No.  3  in  the  same  way  as  the  series  beginning  with 
tree  1.  All  other  forms  of  treatment  were  identical  for  all  trees  and 
the  same  as  during  previous  years. 

7.  Fifth  year. — During  the  fifth  year  the  methods  of  the  fourth 
year  were  continued.  The  trees  were  measured  on  August  15,  1921, 
after  the  growth  of  the  fifth  year  was  almost  completed.  These  meas- 
urements show  that  the  circumference  of  trees  heavily  winter-pruned 
at  the  end  of  the  first,  second,  third,  and  fourth  growing  seasons  was 
only  49  per  cent  of  that  of  the  trees  which  were  not  pruned  at  all; 


Bulletin  348] 


PRUNING  YOUNG  OLIVE  TREES 


95 


Fig.  3. — Second  growing  season.     Typical  trees,  May  29,  1918,  at  13  months. 
Left  column  heavily  winter  pruned.     Middle  and  right  columns,  no  pruning. 


96 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


and  that  the  circumference  of  trees  summer-pruned  during  the  first 
and  second  growing  seasons  and  heavily  pruned  at  the  end  of  the  third 
and  fourth  seasons  was  only  70  per  cent. 

The  depressing  effect  of  heavy  pruning  is  well  shown  by  Fig.  6. 
The  difference  in  size,  i.e.,  total  bulk,  of  the  two  trees  shown  is  esti- 
mated to  be  about  as  100  :10. 


Fig.  4. — Second  winter.     Typical  trees,  January  4,  1919,  at  21  months.     Tree 
to  left  never  pruned.     Tree  to  right  shows  second  pruning. 


THE    RESULTS 

The  experiments  included  three  series  of  36  trees  each,  represent- 
ing different  degrees  of  pruning  or  amounts  of  removal  of  annual 
growth. 

Series  1.     No  pruning.     (N.) 

Series  2.  Summer  pruning  in  the  first  and  second  growing  sea- 
sons and  heavy  winter  pruning  at  the  end  of  the  third  and  fourth 
growing  seasons.      (P.) 

Series  3.  Heavy  winter  pruning  at  the  end  of  the  first,  second, 
third,  and  fourth  growing  seasons.      (PP.) 


Bulletin  348] 


PRUNING  YOUNG  OLIVE  TREES 


97 


Fig.  5. — Second,  third  and  fourth  winters.  Trees  to  right:  top  before  third, 
bottom  before  fourth  pruning.  Trees  to  left:  top  second,  middle  third,  bottom 
fourth  winter  pruning. 


98 


UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 


The  measurements  taken  were : 

The  trunk  circumference  of  four  typical  trees  at  the  end  of  the  first 
growing  season,  when  all  trees  had  received  the  same  treatment. 
(Table  1.) 

The  trunk  circumference  of  all  trees  at  the  end  of  25  months  and 
40  months  after  planting.     (Table  2.) 

The  height  of  all  trees  at  40  months.     (Table  4.) 

1.  Increase  of  circumference  of  trunk. — At  the  end  of  the  first 
growing  season  the  average  size  of  the  trees  was  estimated  from  the 
measurements  shown  in  Table  1. 


Fig.   6. — Result   of   four  winter  prunings   of  young  trees.     A.  Never  pruned. 
B.  Pruned  yearly. 

TABLE  1 

Size  of  Trunk  at  Thirteen  Months  after  Planting 
(Circumference  in  mm.  at  25  cm.  from  ground.) 


Row  2,  tree  10 

Row  2,  tree.  16 

Row  ?,,  tree  13 

Row  4,  tree  16 


PP  N 

52  Row  2,  tree  16  45 

38  Row  2,  tree  17  38 

49  Row  3,  tree  14  38 

19  Row  4,  tree  11  31 


Row  2,  tree  12  41 

Row  2,  tree  18  45 

Row  3,  tree  15  66 

Row  4,  tree  13  29 


Mean  39.5  38.0 

Mean  circumference  of  all  trees  a1  13  months,  41  mm. 


45.3 


Bulletin  318]  PRUNING  YOUNG  OLIVE  TREES  99 

TABLE  2 
Size  of  Trunk  at  Twenty-five  Months  and  at  Forty  Months 
Circumference  of  trunk  in  mm.  at  25  cm.  from  the  ground. 
Tree  Twenty-five  months 


'  PP  N  P  ' 
Row  2 — 

1,   2,   3 85  106  77 

4,   5,   6 90  103 

7,   8,   9 73  118  100 

10,   11,   12 97  159  133 

13,   11,   15 81  155  116 

16,   17,   18 61  112  86 

19,   20,   21 94  70  149 

22.   23,    24 88  87  144 

25.   23,   27 83  156  99 

28,   29,   30 68  173  176 

31,   32,   33 89  123  85 

34.   35.   36 94  130  146 

Row    3 — 

1,   2,   3 80  101  105 

4.    5,   6 89  120  105 

7,   8,   9 94  172  117 

10.    n.   12 121  189 

13.    14,   15 105  203  161 

13,   17,   18 94  132  110 

19.   20,   21 117  187  127 

22.   23,   24 109  110  182 

25.   26,   27 124  180  190 

28,   29,   30 118  145  139 

31,   32,   33 84  177  136 

34,   35,    3d 106  136  109 

Row  4 — 

1,   2,   3 "j  96  85 

4,   5,    6 80  120  36 

7,   8.   9 50  146  59 

10,   11,   12 56  172  129 

13,   14,   15 93  140 

16,   17,   18    68  87 

19,   20,   21 32  71 

22,   23,   24. 44  71  120 

25,   26,   27 94  136  153 

28,   29,   30 ....  72 

31,   32,   33 58  144  126 

34,   35,   36 56  70 


I 

i'orty  months 

A 

PP 

N 

P 

267 

368 

158 

267 

394 

241 

495 

343 

318 

749 

508 

318 

749 

406 

251 

495 

267 

368 

343 

546 

394 

368 

495 

318 

648 

381 

229 

851 

635 

254 

533 

330 

318 

648 

572 

216 

343 

368 

279 

495 

205 

267 

749 

406 

368 

838 

394 

953 

609 

368 

699 

406 

409 

813 

406 

394 

406 

648 

483 

635 

559 

381 

559 

508 

292 

826 

521 

381 

648 

343 

178 

381 

279 

241 

508 

190 

165 

737 

203 

216 

851 

495 

394 

685 

205 

381 

124 

216 

178 

470 

483 

368 

584 
205 

584 

229 

660 

483 

216 

368 

Mean  of  all  trees 84  134  117  295  596  417 

PP  =:  Trees  heavily  pruned  each  year. 

P  =  Trees  lightly  pruned  tAvo  years,  heavily  two  years. 

N  =  Trees  not  pruned. 


3 

4 

(40mo.)t 

40  mo.* 

(437) 

1429 

(357) 

1017 

(351) 

720 

100  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

The  extreme  variation  between  trees  at  the  beginning  was  there- 
fore about  as  100  :29.  At  the  end  of  the  experiment  the  extreme  vari- 
ation was  as  100:13.     (See  table  2.) 

The  extreme  variation  shown  here  between  series  at  the  beginning 
is  as  100:84.  At  the  end  of  the  experiment  it  was  as  100:49.  (See 
Table  2.) 

The  differences  found  between  the  series  can  therefore  be  ascribed 
to  the  difference  in  pruning. 

TABLE  3 

Increase  of  Trunk 
Calculated  from  Tables  1  and  2 

1  2 

13  mo.  25  mo.* 

N— Trees    not    pruned 100  327 

P— Trees  lightly  pruned 100  285 

PP— Trees  heavily   pruned 100  205 

*  Average  circumference,  41  mm.  at  13  months  =  100. 
t  Average  circumference  at  25  months  =  100. 

Table  3  shows  that  heavy  winter  pruning  diminished  the  increase 
in  circumference  of  trunk  37  per  cent  during  the  first  two  years  (PP, 
col.  2)  and  20  per  cent  during  the  second  two  years  (PP,  col.  3),  or  a 
total  retardation  of  50  per  cent  for  the  four  years  (PP,  col.  4). 

Light  summer  pruning  diminished  the  increase  of  circumference 
13  per  cent  during  the  first  two  years  (P,  col.  2).  This  does  not  indi- 
cate that  summer  pruning  is  less  depressing  than  winter  pruning.  The 
summer  pruning  was  very  light  and  the  winter  pruning  heavy.  The 
difference  therefore  indicates  that  the  retardation  bears  a  direct  rela- 
tion to  the  amount  of  foliage  removed. 

Heavy  winter  pruning  during  the  second  two  years  of  trees  not 
winter  pruned  during  the  first  two  (P,  col.  3)  diminished  the  increase 
in  circumference  18  per  cent.  This  corroborates  the  result  with  the 
series  heavily  pruned  every  winter,  which  was  20  per  cent. 

The  retardation  due  to  pruning  during  the  first  two  years  was 
greater  than  during  the  last  two.  As  a  greater  proportion  of  the 
leaves  was  removed  during  the  earlier  years  (see  Figs.  2  and  4),  a 
direct  relation  of  retardation  to  the  amount  of  leaves  removed  is  again 
indicated.  The  large  amount  of  foliage  removed  by  a  heavy  winter 
pruning  is  shown  by  Fig.  5.  In  pruning  the  trees  shown  in  this  figure 
the  part  of  the  foliage  left  was  8.6  per  cent  on  the  two-year-old  trees, 
16  per  cent  on  the  three-year-old,  and  10  per  cent  on  the  four-year-old 
trees. 


Bulletin  348]  pruning  YOUNG  OLIVE  TREES  101 

2.  Increase  of  height  of  tree. — The  height  of  all  the  trees  of  the 
three  series  was  measured  at  40  months.  The  height  was  taken  from 
the  ground  to  the  top  of  the  highest  branches  omitting  single  abnor- 
mally long  twigs. 

TABLE  4 
Height  of  Trees  at  Forty  Months 

Average  height  in  cm.  and  compared  to  that  of  unpruned  trees  taken  as  100. 

N — Trees  unpruned   433  cm.  =  100.0  per  cent 

P — Trees   lightly   pruned 206  cm.  =    47.6  per  cent 

PP — Trees  heavily  pruned 154  cm.  =    35.6  per  cent 

Heavy  pruning  every  year  retarded  increase  of  height  64.4  per 
cent  (PP)  and  during  the  third  and  fourth  years,*  52.4  per  cent  (P). 
The  retardation  of  height  was  therefore  about  twice  the  retardation 
in  circumference  of  trunk.  This  is  opposed  to  the  opinion  of  many 
pruners  who  believe  that  pruning  (cutting  back)  of  the  tops  of  olive 
trees  has  a  tendency  to  increase  growth  in  the  tops  and  thus  increase 
the  height.  The  explanation  is  probably  that  we  are  here  dealing  with 
non-bearing  trees.  With  bearing  trees  the  fruit  borne  on  the  top  of 
the  tree  may  depress  growth  more  than  the  removal  of  leaves. 

3.  Increase  of  hulk  of  tree. — A  comparison  of  the  height  of  the 
trees  or  of  the  circumference  of  the  trunk  gives  an  inadequate  idea  of 
the  difference  in  size  of  the  trees. 

The  areas  of  cross-sections  of  the  trunks  vary  as  the  squares  of  the 
circumferences,  and  these  areas  multiplied  by  the  corresponding 
heights  should  give  a  fair  approximation  of  the  relative  sizes  or  bulks 
of  the  trees.  This  is  the  method  by  which  the  relative  bulk  of  the  trees 
of  the  three  series  has  been  calculated  for  Table  5. 

TABLE  5 

Comparative  Bulk  of  Trees  at  Forty  Months 

(Circumference  squared,  multiplied  by  height;   average  of  unpruned  trees  taken 

as  100) 

Max.  Min.  Mean 

N— Trees  not  pruned 209  4  100 

P — Trees  lightly  pruned 70  2  24 

PP — Trees  heavily  pruned 311  9 

*Some  of  this  retardation  was  probably  due  to  the  summer  pruning  of  the 
first  two  years. 


102  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 

The  retarding  effect  of  severe  winter  pruning  shows  very  clearly 
in  this  table.  Four  primings  reduced  the  average  growth  to  one- 
tenth  of  that  of  an  unpruned  tree,  and  two  primings  to  one-quarter. 

The  trees  which  made  the  smallest  growth — middle  column — were 
undoubtedly  dwarfed  by  mechanical  injuries. 

The  trees  which  were  unpruned  made  a  more  even  growth  than  the 
pruned  trees.  The  difference  between  the  largest  and  the  average,  is 
with  the  unpruned  trees  as  100  :  48,  with  the  trees  pruned  twice,  as 
100  :  34,  and  with  the  trees  primed  four  times  as  100  :  29. 

4.  Attainment  of  desired  form. — The  evidence  shows  that  heavy 
pruning  restricts  the  growth  of  olive  trees  very  greatly  during  the 
first  five  years.  It  indicates  also  that  all  degrees  of  pruning  are 
restrictive  in  proportion  to  their  severity.  It  remains  to  be  seen 
whether  the  object  of  pruning  young  olive  trees — the  attainment  of 
a  desired  form — can  be  accomplished  without  pruning  or  to  what 
degree  pruning  can  be  reduced  without  preventing  the  attainment  of 
this  object. 

An  inspection  of  the  trees  at  4%  years  showed  that  nearly  all  in 
all  three  series  had  main  branches  growing  at  the  desired  angle  of  60°. 
Those  of  the  unpruned  trees,  however,  were  straighter  and  more  regu- 
lar.   The  cause  is  indicated  in  figures  3,  4,  and  5. 

In  figure  3  the  unpruned  trees  commencing  their  second  year's 
growth  are  developing  main  branches  at  angles  varying  from  40°  to 
60°.  In  figure  4  the  unpruned  tree  at  the  end  of  its  second  year's 
growth  has  developed  four  or  five  main  branches  at  almost  exactly 
60°.  In  figure  6  an  unpruned  tree  after  its  fifth  year's  growth  has 
also  its  complement  of  main  branches  at  60°. 

Unpruned  Mission  olives,  therefore,  under  the  conditions  of  the 
experiment,  naturally  develop  main  branches  at  the  desired  angle. 
The  branches  tend  to  be  too  upright  at  first  (Fig.  2),  but  gradually 
spread  (Fig.  3)  until  they  reach  close  to  the  desired  60°  (Fig.  4). 
The  cause  of  this  spreading  is  probably  the  interference  of  the  central 
growth  and  the  weight  of  the  branches  themselves. 

As  the  trees  become  older  and  larger,  the  lower  part  of  these  main 
branches  becomes  thick  and  rigid,  and  they  retain  the  position  reached 
by  the  second  or  third  year. 

In  the  pruned  trees  the  usual  procedure  was  adopted  of  cutting 
out  the  central  twigs  and  branches  to  make  an  open  center,  and  leaving 
the  branches  or  twigs  which  were  growing  most  nearly  at  the  required 
anerle  of  60°. 


Bulletin  348]  PRUNING  YOUNG  OLIVE  TREES  103 

The  defects  of  this  method  are  shown  in  figures  2  and  5.  At  the 
first  pruning  (Fig.  2)  the  two  to  four  branches  left  were  all  at  just 
about  the  required  angle.  During  the  following  summer  the  dense 
growth  in  the  middle  of  the  tree  forced  the  shoots  from  the  branches 
to  extend  too  horizontally.  Later  in  the  season  the  central  shoots 
grew  more  vigorously  than  the  spreading  shoots. 

At  the  second  pruning  (Fig.  5,  upper  tree),  the  strong  growing 
shoots  in  the  middle  of  the  tree  were  removed  and  the  weaker,  spread- 
ing shoots  retained  and  cut  back  to  twigs  growing  most  nearly  in  the 
desired  direction.  In  this  way  the  center  was  made  open  and  the 
twigs  left  were  approximately  at  the  required  angle.  This  method 
gave  the  young  tree  the  required  shape,  but  it  sacrificed  the  most  vigor- 
ous part  of  the  tree,  the  strong  central  shoots. 

The  next  two  summers  and  the  next  two  primings  (Fig.  5,  middle 
and  bottom  trees)  the  same  course  was  followed.  The  result  was 
finally  that  main  branches  were  built  up  in  approximately  the  required 
position.  But  these  branches  were  crooked,  irregular  and  in  every 
way  less  perfect  than  the  branches  on  the  unpruned  trees.  (See 
Fig.  6  b.) 

The  only  apparent  defect  of  form  of  the  unpruned  trees  was  a 
dense  center.  (See  Fig.  6  a.)  This  dense  growth,  however,  up  to 
the  age  of  five  years  has  been  a  great  advantage.  The  unpruned  tree 
(a)  of  figure  6  has  about  ten  times  the  amount  of  foliage  that  the 
pruned  tree  (b)  has  developed.  The  result  is  that  it  is  ten  times  as 
vigorous  and  ten  times  as  capable  of  bearing  crop.  The  leaves  in  the 
center  of  the  tree  were  still  green  and  healthy. 

The  interior  of  the  unpruned  trees  was  undoubtedly  too  shady  for 
the  best  production  of  fruit  but  the  trees  were  not  yet  of  bearing  size. 

5.  Bearing. — Olives  in  central  California  rarely  bear  until  they 
are  four  years  old  and  paying  crops  are  usually  not  obtained  until  the 
sixth  or  seventh  year  after  planting.  The  conditions  at  the  experiment 
plot  are  not  favorable  for  early  bearing. 

At  the  end  of  the  fourth  season  a  few  olives  were  seen  on  an  occa- 
sional tree.  At  the  end  of  the  fifth  enough  were  borne  to  indicate  the 
most  precocious  trees. 

Of  the  33  unpruned  trees  only  5  showed  no  fruit  and  the  remain- 
ing 28  had  about  70  pounds  in  all,  varying  from  a  few  ounces  to  6 
pounds  to  the  tree.  Not  one  olive  was  found  on  any  of  the  pruned 
trees. 


104  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

In  May  of  the  sixth  year,  61  months  after  planting,  an  estimate  of 
the  amount  of  bloom  on  each  tree  was  made.  The  trees  were  classified 
as  follows : 

0  =  No  bloom  or  only  a  trace. 

1  =  Light  bloom. 

2  =  Medium  amount  of  bloom. 

3  =  Full  bloom. 

4  =  Heavy  bloom. 

Number  of  Trees  with  Various  Degrees  of  Bloom 

Bloom  o 

N — No  pruning  2 

P — Light  pruning  26 

PP — Heavy  pruning  33 

Nearly  all  the  unpruned  trees  showed  bloom  irrespective  of  their 
size. 

Most  of  the  pruned  trees  showed  no  bloom  and  none  showed  more 
than  a  small  amount. 

The  relative  fertility  of  the  three  types  of  trees  may  be  expressed 
in  percentages  about  as  follows : 

N — No  pruning,  blossoming 100 

P — Light  pruning,  blossoming 11 

PP — Heavy  pruning,  blossoming 4 

The  influence  of  pruning  on  the  fertility  (blossoming)  of  young 
olive  trees  is  thus  seen  to  be  of  the  same  order  as  its  influence  on  vigor 
(bulk). 


1 

2 

3 

4 

7 

10 

15 

1 

8 

9 

0 

0 

3 

0 

0 

0 

Bulletin  348]  PRUNING  YOUNG  OLIVE  TREES  105 


III.     DEDUCTIONS 

From  these  experiments  it  is  safe  to  formulate  some  general  prin- 
ciples. These  principles,  which  indicate  that  some,  if  not  most,  of  our 
pruning  practices  as  applied  to  young  olives  are  erroneous,  are  a 
valuable  guide  in  devising  better  methods  of  accomplishing  the  object* 
of  pruning. 

PRUNING   A    DETERRENT    OF   GROWTH 

That  both  summer  and  winter  pruning  retarded  the  development 
of  young  olive  trees  has  been  thoroughly  demonstrated.  Whether 
this  retardation  is  due  only  to  the  removal  of  leaves  or  also  to  the 
removal  of  woody  parts  of  the  tree  is  not  shown.  It  seems  reasonable 
to  conclude  that  both  factors  concur  though  the  loss  of  leaves  is  prob- 
ably the  most  important. 

PRUNING   A    DETERRENT   OF   BEARING 

That  pruning  young  olive  trees  also  postpones  bearing  is  evident. 
Pruning,  by  dwarfing  the  trees,  makes  them  less  capable  of  supporfing 
a  large  crop. 

That  none  of  the  pruned  trees  produced  any  fruit  at  the  end  of 
the  fifth  growing  season  while  nearly  all  of  the  unpruned  trees  pro- 
duced a  little  should  not  be  given  much  weight,  because,  as  the  bear- 
ing wood  is  produced  the  previous  year,  and  the  heavy  pruning  re- 
moved nearly  all  the  fruit  buds  all  possibility  of  bearing  was  destroyed. 

However,  that  heavy  pruning  had  prevented  the  production  of 
fruit  buds  was  demonstrated  during  the  sixth  year.  At  the  end  of  the 
fifth  year  all  pruning  was  omitted  on  all  the  trees,  but,  in  spite  of  this, 
practically  no  blossoms  were  borne  during  the  sixth  spring  by  most 
of  the  trees  which  had  been  pruned  during  the  first  four  winters,  while 
nearly  all  the  trees  which  had  never  been  pruned  were  well  loaded 
with  blossoms. 

MINIMIZATION    OF    PRUNING   THE    IDEAL 

Even  though  we  are  convinced  that  the  specific  effect  of  pruning 
is  to  retard  growth  and  bearing,  it  does  not  follow  that  pruning  of  all 
kinds  and  degrees  should  be  abandoned.  There  are  certain  objects  of 
the  grower,  to  compass  which  no  means  has  been  found  except  prun- 
ing. We  should  simply  recognize  this  specific  effect  and  try  to  accom- 
plish our  object  with  as  little  pruning  or  removal  of  leaves  and  other 
parts  of  the  tree  as  possible. 


106  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 


IV.     APPLICATION 

It  has  been  shown  that  under  the  conditions  of  the  experiments  a 
young  olive  will  develop  rapidly  into  a  tree  of  bearing  size  and  nearly 
perfect  shape  without  any  pruning  during  the  first  four  years,  except 
the  removal  of  shoots  on  the  lower  part  of  the  trunk  during  the  first 
two  years.  The  conditions,  however,  were  very  favorable.  The  trees 
used  were  of  the  Mission  variety  which  naturally  takes  the  form 
desired,  and  the  plot  was  well  protected  from  wind. 

Would  this  method  succeed  with  young  trees  of  other  varieties 
and  in  other  weather  conditions  f  Also  what  form  of  pruning  should 
be  adopted  after  the  tree  has  reached  the  size  of  the  tree  shown  in 
Fig.  6a  when  it  can  be  expected  to  begin  to  yield  paying  crops  ? 

DEVELOPMENT   OF   YOUNG   TREES 

In  situations  where  the  trees  are  subjected  to  heavy  prevailing 
winds  it  would  doubtless  be  necessary  to  support  them  with  a  stout 
7  or  8-foot  stake  during  the  first  two  or  three  growing  seasons.  It 
might  be  advisable  also  to  shorten  the  branches  on  the  leeward  side 
to  encourage  them  to  grow  more  upright  and  to  throw  more  growth 
into  the  branches  on  the  windward  side. 

With  spreading  trees,  such  as  the  Manzanillo  and  Ascolano,  the 
main  branches  tend  to  grow  horizontal.  This  can  be  overcome  by 
tying  these  horizontal  branches  to  each  other  by  a  stout  cord  or  band 
of  burlap  passing  through  the  center  of  the  tree.  A  stake  would  also 
be  necessary  in  this  case.  After  a  branch  has  been  held  in  the  right 
position  in  this  way  for  one  year,  it  becomes  rigid  and  will  maintain 
the  angle  given. 

This  tying  should  commence  at  the  end  of  the  first  growing  season 
and  should  be  continued  for  one  or  two  years  more.  If  neglected 
until  the  branches  are  over  half  an  inch  thick  their  angle  cannot  be 
changed  without  danger  of  breaking. 

MAINTENANCE    OF    BEARING    TREES 

When  a  tree  reaches  the  size  and  form  shown  in  Figures  6  a  and 
7  a  it  is  ready  to  be  treated  as  a  bearing  tree. 

As  a  bearing  tree  it  has  too  dense  a  mass  of  foliage  and  lacks  the 
open  center  which  its  desirable.  Figure  7  shows  how  such  a  tree  can 
be  very  easily  given  the  required  form. 


Bulletin  348] 


PRUNING  YOUNG  OLIVE  TREES 


107 


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108  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 

First,  one  or  more  of  the  central  branches  are  removed  entirely 
at  their  origin  on  the  trunk  or  on  the  base  of  another  large  branch, 
leaving  a  hollow  center  and  a  ring  of  branches  rising  at  about  the 
desired  angle  of  60°.  Usually  this  ring  of  branches  will  be  too  dense 
and  some  of  them  should  be  removed  in  the  same  way,  taking  care  to 
have  the  reserved  branches  as  equally  spaced  as  possible.  All  this 
work  is  done  with  a  good  sharp  pruning  saw  and  requires  from  5  to 
10  minutes.     The  tree  has  then  the  form  shown  in  figure  7  b. 

On  certain  parts  of  the  tree  after  the  saw-pruning  there  will  be 
too  dense  a  mass  of  twigs  and  foliage.  This  must  be  thinned  out  with 
a  pair  of  small  one-hand  shears.  The  densest  parts  of  the  tree  will 
usually  be  low  down,  from  near  the  ground  to  the  height  of  the 
shoulder.  The  thinning  out  does  not  require  very  precise  work.  It 
should  consist  in  "cutting  out"  entirely  twigs  and  small  branchlets, 
not  in  "topping"  or  "cutting  back."  Branchlets  which  reach  the 
ground  should  first  be  removed  and  then  enough  of  the  rest  to  let 
daylight  through  into  all  parts  of  the  tree.  Little  or  no  thinning 
should  be  done  on  the  upper  part  of  the  tree.  The  removal  of  main 
branches  with  the  saw  usually  opens  up  the  top  sufficiently.  This 
thinning  will  take  two  or  three  times  as  long  as  the  saw  work.  When 
finished  the  tree  should  have  the  appearance  shown  in  figure  7  c. 

The  age  at  which  the  first  pruning  should  be  done  will  depend  on 
the  rapidity  with  which  the  tree  develops.  Figure  8  shows  a  border 
tree,  six  years  old,  which  has  just  reached  the  stage  of  development 
at  which  the  first  pruning  appears  advisable.  If  the  pruning  is  done 
too  early  the  development  of  the  tree  is  retarded.  If  it  is  done  too 
late  the  wounds  made  in  opening  up  the  interior  will  be  unnecessarily 
large  and  the  bearing  twigs  in  the  interior  will  commence  to  weaken 
through  lack  of  sunlight. 

The  correct  stage  seems  to  be  when  the  tree  is  large  enough  to 
produce  a  paying  crop  without  danger  of  overtaxing  its  energies.  This 
is  a  matter  of  judgment  based  on  experience.  This  stage  will  be 
reached  in  well-handled  orchards  at  the  fourth,  fifth,  or  sixth  year, 
according  to  the  soil,  climate  and  variety. 


Bulletin  348] 


PRUNING  YOUNG  OLIVE  TREES 


109 


V.     SUMMARY  AND   CONCLUSIONS 

1.  Pruning  retards  the  growth  of  olive  trees,  especially  when  they 
are  young.  The  excessive  pruning  often  practiced  on  young  trees 
may  retard  their  development  90  per  cent. 


Fig.  8. — First  pruning  at  six  years.     A.  Mission  tree  six  years  old  in  a  row  of 
border  trees — never  pruned.     B.  Same  tree  after  first  pruning  at  six  years. 

2.  Mission  olives  which  receive  no  pruning  during  the  first  four 
or  five  years  develop  a  more  perfect  form  than  pruned  trees. 

3.  The  method  of  handling  young  Mission  olives  recommended  on 
the  basis  of  five  years'  experiments  hastens  the  development  of  the 
trees,  improves  their  form,  promotes  early  bearing,  and  saves  the 
whole  expense  of  pruning  for  four  or  five  years. 

4.  The  method  is  probably  applicable  to  any  varieties  of  naturally 
upright  habit. 


110  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

5.  The  use  of  stakes  and  tying  may  be  required  during  the  first 
two  or  three  years  with  varieties  of  spreading  habit  like  the  Manza- 
nillo  and  Ascolano.  This  expense  would  be  offset  by  the  saving  in 
pruning  and  the  improved  form  of  the  tree,  and  the  more  rapid  devel- 
opment would  be  a  net  gain. 


ACKNOWLEDGMENTS 

The  planting  and  pruning  and  much  of  the  note-taking  in  the 
experiments  were  done  by  Messrs.  F.  Flossfeder  and  G.  Barovetto, 
without  whose  efficient  cooperation  the  work  could  not  have  been 
done. 

Valuable  assistance  was  also  rendered  by  Messrs.  W.  F.  Oglesby, 
L.  0.  Bonnet  and  A.  J.  Winkler. 


STATION  PUBLICATIONS  AVAILABLE   FOR  FREE   DISTRIBUTION 


BULLETINS 


No. 

251.  Utilization  of  the  Nitrogen  and  Organic 
Matter  in  Septic  and  Imhoff  Tank 
Sludges.  . 

253.  Irrigation  and  Soil  Conditions  in  the 
Sierra  Nevada  Foothills,  California. 

261.  Melaxuma    of    the    Walnut,    "Juglans 

regia." 

262.  Citrus  Diseases  of  Florida   and   Cuba 

Compared  with  Those  of  California. 

263.  Size  Grades  for  Ripe  Olives. 

267.  Experiments  with  Stocks  for  Citrus. 

268.  Growing  and  Grafting  Olive  Seedlings. 

270.  A  Comparison  of  Annual  Cropping,  Bi- 
ennial Cropping,  and  Green  Manures 
on  the  Yield  of  Wheat. 

273.  Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain. 

275.  The  Cultivation  of  Belladonna  in  Cali- 

fornia. 

276.  The  Pomegranate. 

278.  Grain  Sorghums. 

279.  Irrigation  of  Rice  in  California. 

280.  Irrigation  of  Alfalfa  in  the  Sacramento 

Valley. 

282.  Trials  with  California  Silage  Crops  for 

Dairy  Cows. 

283.  The  Olive  Insects  of  California. 

285.  The  Milk  Goat  in  California. 

286.  Commercial  Fertilizers. 

287.  Vinegar  from  Waste  Fruits. 
294.   Bean  Culture  in  California. 

297.  The  Almond  in  California. 

298.  Seedless  Raisin  Grapes. 

299.  The  Use  of  Lumber  on  California  Farms. 
304.  A  Study  on  the  Effects  of  Freezes  on 

Citrus  in  California. 
308.   I.  Fumigation  with  Liquid  Hydrocyanic 
Acid.  II.  Physical  and  Chemical  Prop- 
erties of  Liquid  Hydrocyanic  Acid. 


No. 

309. 

310. 
312. 
313. 
316. 
317. 

320. 
321. 
323. 

324. 

325. 


330. 
331. 
332. 
334. 

335. 

336. 

337. 
339. 

340. 

341. 
342. 
343. 
344. 

347. 

348, 


I.  The  Carob  in  California.     II.  Nutri- 
tive Value  of  the  Carob  Bean. 
Plum  Pollination. 
Mariout  Barley. 

Pruning  Young  Deciduous  Fruit  Trees. 
The  Kaki  or  Oriental  Persimmon. 
Selections  of   Stocks  in   Citrus  Propa- 
gation. 
Control  of  the  Coyote  in  California. 
Commercial  Production  of  Grape  Syrup. 
Heavy    vs.    Light    Grain    Feeding    for 

Dairy  Cows. 
Storage  of  Perishable  Fruit  at  Freezing 

Temperatures. 
Rice  Irrigation  Measurements  and  Ex- 
periments    in     Sacramento     Valley, 
1914-1919. 
Dehydration  of  Fruits. 
Phylloxera-Resistant  Stocks. 
Walnut  Culture  in  California. 
Preliminary  Volume  Tables  for  Second- 
Growth  Redwoods. 
Cocoanut   Meal    as    a    Feed   for   Dairy 

Cows  and  Other  Livestock. 
The  Preparation  of  Nicotine  Dust  as 

an  Insecticide. 
Some  Factors  of  Dehydrater  Efficiency. 
The  Relative  Cost  of  Making  Logs  from 

Small  and  Large  Timber. 
Control  of  the  Pocket  Gopher  in  Cali- 
fornia. 
Studies  on  Irrigation  of  Citrus  Groves. 
Hog  Feeding  Experiments. 
Cheese  Pests  and  Their  Control. 
Cold  Storage  as  an  Aid  to  the  Market- 
ing of  Plums. 
The  Control  of  Red  Spiders  in  Decidu- 
ous Orchards. 
Pruning  Young  Olive  Trees. 


CIRCULARS 


No. 

70. 

82. 

87. 
110. 
111. 

113. 
115. 
126. 
127. 
129. 
138. 
144. 
148. 
151. 
152. 

155. 
157. 
159. 
161. 
164. 
165. 

166 
167 
169 
170 


No. 

Observations    on    the    Status    of    Corn  172. 
Growing  in  California.  173. 
The  Common  Ground  Squirrels  of  Cali- 
fornia. 174. 
Alfalfa.  175. 

Green  Manuring  in  California. 

The  Use  of  Lime  and  Gypsum  on  Cali-  178. 

fornia  Soils.  179. 

Correspondence  Courses  in  Agriculture. 

Grafting  Vinifera  Vineyards.  181. 

Spraying  for  the  Grape  Leaf  Hopper. 

House  Fumigation.  182. 

The  Control  of  Citrus  Insects. 

The  Silo  in  California  Agriculture.  183. 

Oidium  or  Powdery  Mildew  of  the  Vine.  184. 

"Lungworms."  188. 

Feeding  and  Management  of  Hogs.  189. 

Some  Observations  on  the  Bulk  Hand-  190. 

ling  of  Grain  in  California.  193. 

Bovine  Tuberculosis.  198. 

Control  of  the  Pear  Scab.  201. 

Agriculture  in  the  Imperial  Valley.  202. 

Potatoes  in  California. 

Small  Fruit  Culture  in  California.  203. 

Fundamentals   of   Sugar  Beet   Culture  205. 

under  California  Conditions.  206. 

The  County  Farm  Bureau.  208. 

Feeding  Stuffs  of  Minor  Importance. 

The  1918  Grain  Crop.  209. 

Fertilizing  California  Soils  for  the  1918  210. 

Crop.  212. 


Wheat  Culture. 

The    Construction    of    the    Wood-Hoop 

Silo. 
Farm  Drainage  Methods. 
Progress  Report  on  the  Marketing  and 

Distribution  of  Milk. 
The  Packing  of  Apples  in  California. 
Factors    of    Importance    in    Producing 

Milk  of  Low  Bacterial  Count. 
Control     of     the     California     Ground 

Squirrel. 
Extending  the  Area  of  Irrigated  Wheat 

in  California  for  1918. 
Infectious  Abortion  in  Cows. 
A  Flock  of  Sheep  on  the  Farm. 
Lambing  Sheds. 
Winter  Forage  Crops. 
Agriculture  Clubs  in  California. 
A  Study  of  Farm  Labor  in  California. 
Syrup  from  Sweet  Sorghum. 
Helpful  Hints  to  Hog  Raisers. 
County   Organizations   for   Rural   Fire 

Control. 
Peat  as  a  Manure  Substitute. 
Blackleg. 
Jack  Cheese. 
Summary  of  the  Annual  Reports  of  the 

Farm  Advisors  of  California. 
The  Function  of  the  Farm  Bureau. 
Suggestions  to  the  Settler  in  California. 
Salvaging  Rain-Damaged  Prunes. 


No.  No. 

214.  Seed  Treatment  for  the  Prevention  of  236. 

Cereal  Smuts. 

215.  Feeding  Dairy  Cows  in  California. 

217.  Methods   for  Marketing   Vegetables   in  237. 

California. 

218.  Advanced    Registry    Testing    of    Dairy  238. 

Cows.  239. 

219.  The  Present  Status  of  Alkali. 

223.  The  Pear  Thrips.  240. 

224.  Control    of   the    Brown    Apricot    Scale 

and  the  Italian  Pear  Scale  on  Decid-  241. 

uous  Fruit  Trees. 

225.  Propagation  of  Vines.  242. 

227.  Plant  Diseases  and  Pest  Control.  243. 

228.  Vineyard  Irrigation  in  Arid  Climates. 

230.  Testing  Milk,   Cream,    and   Skim  Milk  244. 

for  Butterfat.  245. 

231.  The  Home  Vineyard.  246. 

232.  Harvesting    and    Handling    California 

Cherries  for  Eastern  Shipment.  247. 

233.  Artificial  Incubation.  248. 

234.  Winter  Injury  to  Young  Walnut  Trees 

during  1921-22.  249. 

235.  Soil  Analysis  and  Soil  and  Plant  later-  252. 

relations.  253. 


The  Common  Hawks  and  Owls  of  Cali- 
fornia from  the  Standpoint  of  the 
Rancher. 

Directions  for  the  Tanning  and  Dress- 
ing of  Furs. 

The  Apricot  in  California. 

Harvesting  and  Handling  Apricots  and 
Plums  for  Eastern  Shipment. 

Harvesting    and    Handling    Pears    for 

,    Eastern   Shipment. 

Harvesting  and  Handling  Peaches  for 
Eastern   Shipment. 

Poultry  Feeding. 

Marmalade  Juice  and  Jelly  Juice  from 
Citrus  Fruits. 

Central  Wire  Bracing  for  Fruit  Trees. 

Vine  Pruning  Systems. 

Desirable  Qualities  of  California  Bar- 
ley for  Export. 

Colonization  and  Rural  Development. 

Some  Common  Errors  in  Vine  Pruning 
and  Their  Remedies. 

Replacing  Missing  Vines. 

Supports  for  Vines. 

Vineyard  Plans. 


